Conventional medical suction apparatus have included canister and lid assemblies with a suction port and a patient port, each extending through the lid. Typically, a vacuum pump is connected to the suction port, and a tube is connected between the patient and the patient port. The suction of the vacuum pump is then transmitted through the suction port, through the canister and through the patient port to withdraw fluids from the patient during a medical procedure. The fluid enters the canister through the patient port. When the fluid rises to a predetermined level, a shut off valve blocks the suction port eliminating the suction at the patient port and preventing additional fluid from being withdrawn from the patient.
Shut off valves used in such medical suction apparatus are known to have included plungers connected to a float for moving upwardly in response to the rising fluid level within the canister to block the suction port. One type of plunger previously used included an inwardly tapered upper end. When the fluid within the canister rose to a predetermined level, the tapered end of the plunger moved upwardly and was forced into the suction port to block or shut off the suction. This type of plunger suffered from a misalignment problem. If the suction port and the plunger were out of alignment, it was possible that the plunger would engage other lid structure, and the tapered portion of the plunger would not be inserted into the suction port. In such event, the suction port would not be sealed, and fluid would continue to be withdrawn from the patient until the canister overflowed. Also, this type of plunger was associated with a problem of foreign material becoming lodged between the tapered end of the plunger and the suction port. The foreign material would prevent proper sealing of the plunger against the suction port, and, again, the medical suction apparatus would continue to function until the canister was overflowing.
Another type of plunger known to have been used in a shut off valve for a medical suction apparatus included a float connected to a hard plastic plunger having a small plastic post extending upwardly from the upper end of the plunger. Typically, the upper end of the post included an enlarged head or retainer ring, and a rubber disc having a small aperture at its center was mounted on the post by deforming the disc to insert the post into the aperture. The deformation of the disc when mounted on the post caused the disc to form an upwardly facing suction cup. When the plunger was forced upwardly by rising fluid in the canister, the rubber disc covered and blocked the suction port. In the use of this type of plunger and cup assembly, leakage was found to occasionally occur between the post and the rubber disc. This problem necessitated testing each valve to insure proper functioning. Also, an excessive amount of hand labor was required to deform and place the disc on the post.
Thus, a need has arisen for a shut off valve employing a suction cup to block the suction port that may be manufactured with reduced hand labor. Also, a need has arisen for a plunger and suction cup assembly that combines the economies of manufacturing by molding with the effectiveness of a suction cup shut off valve. Furthermore, a need has arisen for a suction cup and plunger for use in a shut off valve that reliably provides a nonleaking seal covering the shut off port such that individual testing of each valve will not be necessary and that may be used without a separate float, if desired.